Android弹幕编程设计实现的解决方案（一）

Android弹幕编程设计实现的解决方案（一）

在现在的一些视频类网站、视频类直播网站，比如A站和B站，当视频在播放的时候，会在屏幕上出现一些滚动的字幕，这些字幕是UGC，通常是用户的评论，称之为“弹幕”，这些弹幕一般从右往左滚动，以符合人类的阅读习惯。
现在给出一个实现Android平台上的弹幕编程设计实现方案。
（1）要注意的是，一般视频播放是一个view，比如是VideoView，弹幕是在VideoView上面滚动，这就要求弹幕必须和VideoView完全密合在一起，至少在视觉上让用户看上去觉得这就是直接在视频画面上写上去的。那么在下面的这个例子中，就干脆直接继承自一个相对布局RelativeLayout。因为是一个布局文件，如果使用VideoView这类的播放器，就好办了，直接设置view的layout宽和高均为match_parent即可。
（2）弹幕一般是随机批量显示。我观察了一些热门网站的弹幕显示，它们是随机的，我在处理弹幕字幕文本时候，设计了一个set方法，一次性批量喂给弹幕一个数据池子（实际上就是在弹幕类里面的一个LinkedList数据队列texts），让弹幕从这些池子中每次随机抽出一个显示。假设上层应用的文本有更新（比如用户有新的评论添加进来），直接追加到队列头部。

以下是全部源代码实现。
核心关键的弹幕相对布局BarrageRelativeLayout.java：

package zhangphil.demo;import android.content.Context;
import android.graphics.Color;
import android.graphics.Rect;
import android.os.Handler;
import android.os.Message;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.animation.AccelerateDecelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;
import android.widget.RelativeLayout;
import android.widget.TextView;import java.util.LinkedList;
import java.util.Random;public class BarrageRelativeLayout extends RelativeLayout {private Context mContext;private Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);if(msg.what==RANDOM_SHOW) {String text = texts.get(random.nextInt(texts.size()));BarrageTextItem item = new BarrageTextItem(text);showBarrageItem(item);//每个弹幕产生的间隔时间随机int duration = (int) ((BARRAGE_GAP_MAX_DURATION - BARRAGE_GAP_MIN_DURATION) * Math.random());this.sendEmptyMessageDelayed(RANDOM_SHOW, duration);}}};public static int RANDOM_SHOW=0x0a1;public static int SEQ_SHOW=0x0a2;private Random random = new Random(System.currentTimeMillis());private static final long BARRAGE_GAP_MIN_DURATION = 1000;//两个弹幕的最小间隔时间private static final long BARRAGE_GAP_MAX_DURATION = 2000;//两个弹幕的最大间隔时间private int maxSpeed = 10000;//速度，msprivate int minSpeed = 5000;//速度，msprivate int maxSize = 30;//文字大小，dpprivate int minSize = 15;//文字大小，dpprivate int totalHeight = 0;private int lineHeight = 0;//每一行弹幕的高度private int totalLine = 0;//弹幕的行数private LinkedList<String> texts = null;public BarrageRelativeLayout(Context context) {this(context, null);}public BarrageRelativeLayout(Context context, AttributeSet attrs) {this(context, attrs, 0);}public BarrageRelativeLayout(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);mContext = context;init();}private void init() {texts = new LinkedList<String>();}public void show(int type){int duration = (int) ((BARRAGE_GAP_MAX_DURATION - BARRAGE_GAP_MIN_DURATION) * Math.random());mHandler.sendEmptyMessageDelayed(type, duration);}//显示一批弹幕文本//相当于给弹幕设置数据源public void setBarrageTexts(LinkedList<String> texts) {this.texts = texts;}//头部第一个位置追加，最新的。public void addBarrageText(String text) {this.texts.add(0,text);}@Overridepublic void onWindowFocusChanged(boolean hasWindowFocus) {super.onWindowFocusChanged(hasWindowFocus);totalHeight = getMeasuredHeight();lineHeight = getLineHeight();totalLine = totalHeight / lineHeight;}private void showBarrageItem(final BarrageTextItem item) {int leftMargin = this.getRight() - this.getLeft() - this.getPaddingLeft();LayoutParams params = new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);params.addRule(RelativeLayout.ALIGN_PARENT_TOP);params.topMargin = item.verticalPos;this.addView(item.textView, params);Animation anim = generateTranslateAnim(item, leftMargin);anim.setAnimationListener(new Animation.AnimationListener() {@Overridepublic void onAnimationStart(Animation animation) {}@Overridepublic void onAnimationEnd(Animation animation) {item.textView.clearAnimation();BarrageRelativeLayout.this.removeView(item.textView);}@Overridepublic void onAnimationRepeat(Animation animation) {}});item.textView.startAnimation(anim);}private TranslateAnimation generateTranslateAnim(BarrageTextItem item, int leftMargin) {TranslateAnimation anim = new TranslateAnimation(leftMargin, -item.textMeasuredWidth, 0, 0);anim.setDuration(item.moveSpeed);anim.setInterpolator(new AccelerateDecelerateInterpolator());anim.setFillAfter(true);return anim;}/*** 计算TextView中字符串的长度** @param text 要计算的字符串* @param Size 字体大小* @return TextView中字符串的长度*/public float getTextWidth(BarrageTextItem item, String text, float Size) {Rect bounds = new Rect();TextPaint paint;paint = item.textView.getPaint();paint.getTextBounds(text, 0, text.length(), bounds);return bounds.width();}/*** 获得每一行弹幕的最大高度** @return*/private int getLineHeight() {BarrageTextItem item = new BarrageTextItem();//传递进去一个非空字符串，目的是为了获得一个计算值String tx = "no null data";item.textView = new TextView(mContext);item.textView.setText(tx);item.textView.setTextSize(maxSize);Rect bounds = new Rect();TextPaint paint;paint = item.textView.getPaint();paint.getTextBounds(tx, 0, tx.length(), bounds);return bounds.height();}//弹幕的一个文本itempublic class BarrageTextItem {public TextView textView;public int textColor;public String text;public int textSize;public int moveSpeed;//移动速度public int verticalPos;//垂直方向显示的位置public int textMeasuredWidth;//字体显示占据的宽度public BarrageTextItem() {}public BarrageTextItem(String text) {this.textSize = (int) (minSize + (maxSize - minSize) * Math.random());this.text = text;this.textColor = Color.rgb(random.nextInt(256), random.nextInt(256), random.nextInt(256));this.textView = new TextView(mContext);textView.setText(text);textView.setTextSize(textSize);textView.setTextColor(textColor);textMeasuredWidth = (int) getTextWidth(this, text, textSize);moveSpeed = (int) (minSpeed + (maxSpeed - minSpeed) * Math.random());if (totalLine == 0) {totalHeight = getMeasuredHeight();lineHeight = getLineHeight();totalLine = totalHeight / lineHeight;}verticalPos = random.nextInt(totalLine) * lineHeight;}}
}

直接写进布局当作一个一般的相对布局使用：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context="zhangphil.demo.MainActivity"><zhangphil.demo.BarrageRelativeLayoutandroid:id="@+id/barrageView"android:layout_width="match_parent"android:layout_height="match_parent"android:background="@android:color/white" /></RelativeLayout>

上层activity使用方法：

package zhangphil.demo;import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;import java.util.LinkedList;public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);BarrageRelativeLayout mBarrageRelativeLayout = (BarrageRelativeLayout) findViewById(R.id.barrageView);String[] itemText = {"zhangphil@csdn 0", "zhangphil 1", "zhang phil 2","zhang 3","phil 4","zhangphil ... 5", "***zhangphil 6", "zhang phil csdn 7", "zhang ... phil 8", "phil... 9", "http://blog.csdn.net/zhangphil 10"};LinkedList<String> texts=new LinkedList<String>();for(int i=0;i<itemText.length;i++){texts.add(itemText[i]);}mBarrageRelativeLayout.setBarrageTexts(texts);mBarrageRelativeLayout.show(BarrageRelativeLayout.RANDOM_SHOW);}
}

代码运行结果（弹幕从右往左滚动显示）：